1. Field of the Invention
This invention relates to a method for producing a portable data carrier having a surface structure embossed at least in certain areas on one side, the data carrier being produced by joining a plurality of layers.
2. Description of the Background Art
To impede or prevent forgery or manipulation of data carriers such as ID cards, credit cards, Eurocheque cards or the like, such data carriers are provided with special security features. The security features used are preferably ones having a striking, readily visible but uncopiable visual effect, on the one hand, and allowing maximally cost-effective production of the data carriers, on the other hand. Such a security feature is for example a surface structure embossed into the surface of an ID card in the form of a lens structure through which different images, so-called “tilt images,” are visible at different angles of vision. The lens structure is embossed into a transparent cover layer of the data carrier. It is preferably a cylindrical lens screen. Through said lens screen, information is incorporated by means of a laser into volume areas of the data carrier body located thereunder, said information being readily recognizable visually as blackened areas. Due to the focal effect of the lenses, only narrowly limited areas of the data carrier are blackened so that the information can only be observed at the viewing angle corresponding to the angle of incidence of the laser on the lens structure. It is thus possible to use different inscription angles to inscribe several pieces of information each recognizable only at certain viewing angles, thereby producing the “tilt image” effect. Such security features are known as MLIs (multiple laser images). MLIs are either difficult or impossible to copy, so that forgeries or manipulated data carriers are recognizable immediately and without great effort.
The abovementioned data carriers having a multilayer, i.e. at least two-layer, structure—as is usually the case with chip cards—are normally produced by a laminating plate technology by which the individual data carrier layers are placed one above the other between two laminating plates and laminated under the action of heat and pressure. DE 196 47 153 A1 describes methods for producing a surface structure on the multilayer data carrier to be produced simultaneously with the laminating process by means of an embossing structure formed on the laminating plate. In addition it states methods by which a thermostable embossing plate is inserted between the cover layer of the data carrier and the laminating plate during the laminating process.
A further possibility for producing the abovementioned data carriers is to emboss the finished single cards after production.
All these known methods of embossing the surface structure into the finished data carrier during or after the laminating process have the disadvantage that the embossing process can fundamentally damage the data carrier in the form of warps and deformations. This considerably increases the reject rate during production.